Device-to-device audio communication (think QR codes, but made out of sound) seems very underrated. Much better UX than QR codes or NFC because you don't have to worry about putting your phone in the exactly right place or pointing it in the right direction.

Anyone here with more detailed takes on this?

They had something similar in Japan when I was living there before smartphones were a thing, in 2008-2009. Basically, you would ask your phone to exchange contact details with another, and hold their wireless sensor next to the other phone's sensor, and boom, done. 

It was a nice social ritual too.